Flow Regimes in Vertical and Inclined Oil/Water Flow in Pipes

Abstract

Abstract Flow regime behavior in upwards oil-water flow has been studied in a large diameter, inclinable, multiphase flow loop. With the pipe vertical, bubble flow occurred for all conditions tested. When the pipe was inclined by 5 or 150 from vertical, a new flow regime, countercurrent bubble flow, was observed over a wide range of flow conditions. Theoretical flow regime maps developed for gas-liquid flow did not properly predict oil-water flow regime behavior. Introduction Two-phase flows are generally characterized by their flow regimes - a description of the distribution of the phases in the pipe. For gas-liquid flow, numerous studies have shown that certain characteristic flow regimes exist and that important properties of the flow such as the in-situ fractions of the phases present and the pressure drop behavior depend strongly on the flow regime. Recently, mechanistic models of flow regime transitions have been developed to predict the flow regime that will occur for a given set of flow rates and fluid properties. It has been suggested that some of these models should be applicable to liquid-liquid flows, yet little data exists to support these claims. For oil-water flow, procedures such as pressure drop calculations and interpretation of production logs require knowledge of flow regime behavior, but only a few studies in small diameter pipes are available to provide such information. We have conducted a series of tests of oil-water flow in a 42 ft long, 7-1/4 in. diameter inclinable flow loop to characterize the flow regime behavior in oil-water flow. We have studied flow rates up to 5020 B/D of each phase with the pipe vertical and inclined 5 and 150 from vertical. In each experiment the flow rates of each phase were set and allowed to stabilize. Then the flow was videotaped through the plexiglass pipe. The flow regime behavior differed markedly from gas-liquid flow. In vertical flow, three flow regimes were observed: a bubble flow having large bubbles of oil dispersed in the continuous water phase; a dispersed bubble flow, in which extremely small oil bubbles were dispersed in the water; and an inverted bubble flow, consisting of water droplets entrained in a continuous oil phase. phase. When the pipe was inclined, different flow regimes from any previously described were observed. The phase distribution still consisted of bubbles of one phase distributed in the other phase, but a phase distributed in the other phase, but a countercurrent stream of the denser phase was observed flowing downward along the lower side of the pipe. The upper side of the pipe had a high pipe. The upper side of the pipe had a high concentration of the less dense phase moving at relatively high velocities. Thus, these inclined flow patterns are characterized by a highly nonuniform patterns are characterized by a highly nonuniform velocity profile with a high upwards velocity on the upper side of the pipe, a net zero flow point somewhere in the central portion of the pipe, and a downwards velocity on the lower side of the pipe. FLOW REGIMES AND FLOW REGIME MAPS Important properties of two-phase flow such as the holdup of the dense phase and the pressure gradient depend strongly on the distribution of the phases in the pipe. Thus, many researchers have tried phases in the pipe. Thus, many researchers have tried to identify the various flow patterns or flow regimes that occur. The description of these patterns is obviously somewhat arbitrary in nature, and many different names have been used in labeling them. In gas-liquid vertical upwards flow, four flow patterns are now generally agreed upon in the two-phase flow literature - bubble, slug, churn, and annular flow. P. 361